1. Field of the Invention
This invention relates generally to a battery saver circuit for use with a paging receiver, which saver circuit is provided for periodically supplying power to the receiver in short bursts instead of continuously and for keeping the receiver on in the event that the presence of code signals is detected which signals are transmitted subsequently after a preamble.
2. Description of the Prior Art
Radio paging systems have proven very popular and many efforts have been made to reduce their size, weight, and power consumption through the use of integrated circuits.
In connection with power conservation, battery saving circuits are used to minimize power consumption by periodically supplying power to a receiver in short bursts instead of continuously. Presently known battery saver circuits operating in such a radio pager receiver periodically supply power, enabling the search for the presence of a preamble code. If the preamble code is found, then they extend the time period for predetermined sequential codes.
This prior art will further be explained with reference to FIGS. 1A-1C.
FIG. 1A shows a code sequence transmitted from a calling station, wherein a preamble P with a time period T is followed by message and end codes (A and E respectively). FIG. 1B shows pulses B' each having a time period T1 which represents the time duration for which power is supplied to high power drain circuits of the receiver. During this time period T1, the pager receiver is rendered operative and is permitted to search for the preamble. The time periods T1, T2 (power on and off periods respectively) occur sequentially and are chosen to satisfy the equation (2T1+T2=T) so that each of the repetitive pulses B must occur within the duration of a preamble. FIG. 1C shows the application of power to the pager receiver as a result of the detection of the preamble.
FIG. 2 shows a standard code format proposed by the POCSAG (British Post Office Code Standardisation Advisory Group). According to the specification of the POCSAG, a transmission consists of a preamble P followed by batches 1, 2, 3, . . . , each batch beginning with a synchronization codeword (SC). The transmission ceases when there are no further calls. Each transmission starts with a preamble to permit the pages to attain bit synchronization and to prepare them to acquire word synchronization. The preamble is a pattern of reversals, 101010 . . . , repeated for a period of at least 576 bits, i.e., the duration of a batch plus a codeword. Codewords are transmitted in batches each of which comprises an SC followed by 8 groups or frames each containing 2 codewords. The detailed explanation of the above, is given in the document entitled "A Standard Code for Radiopaging" (available from: Telecommunications Development Department, TD4.2.3. 2-12 Gresham Street, London EC2V7AG, United Kingdom).
In the transmission system of the POCSAG, the preamble is added to the head of a new sequence of calling signals whereby if continuous callings occur then another preamble is not transmitted until the interruption of the callings and the occurrence of the next new signal transmission. Thus, there exists the possibility that only one preamble is transmitted in a day due to an uninterrupted sequence of calls. This means that if the foregoing power consumption technique, in which power is supplied periodically, is applied to the pager receiver operable on the POCSAG code signals, a subscriber may miss the reception of his caller's message. More specifically, if a subscriber switches on to energize his pager after the preamble has already been transmitted, he can no longer receive any message signals. A similar problem may also be encountered when a subscriber is within a building, in the subway or the like where paging signals are too weak to be receive and the preamble goes undetected.
Although the code signals proposed by the POCSAG has been exemplified in the above, similar problems may be encountered with a radio paging system wherein a preamble is added to the head of a new sequence of calling signals and the next preamble is not transmitted until the interruption of the sequence and the occurrence of the next new signal transmission.